Miscible flooding process

ABSTRACT

A miscible flooding process for the recovery of oil from subterranean petroleum reservoirs containing excessive amounts of monovalent and polyvalent metal salts in which a specially formulated soluble oil is injected into the reservoir through one or more injection wells, and thereafter displaced through the reservoir towards one or more spaced production wells by the subsequent injection of an aqueous flooding medium. The soluble oil comprises an admixture of a liquid hydrocarbon, surface active alkyl aryl sulfonates, an organic stabilizing agent, and an alkali metal or ammonium salt of a sulfated alkyl primary alcohol ethoxylate having 12 to 16 carbon atoms in the alkyl group. The soluble oil can be substantially anhydrous, or it can contain water present in the form of a water-in-oil microemulsion.

rated States Patent 1191 1111 3,

Holm [451 Nov. 18, 1975 MISCIBLE FLOODING PROCESS 3,811,504 5/1974Flournoy etal. 166/273 3,811,505 5/1974 Flourno et al. 166/273 [75]Inventor Leroy Fullerton Cahf- 3,811,507 5/1974 Flournoz et a1v 166/273Assignee: Union Company of Calif r ia, DyCUS et al. Brea, Calif. P E S hJ N d rzmarv .rammerte en ovosa [22] Flled: 1973 AssistantExamirier-Jafk E. Ebel [21] A N 345,184 Attorney, Agent, or Firm-DeanSandford; Richard C.

Hartman; Lannas S. Henderson [52] US. Cl. 166/274; 166/275; 252/855 D 51Int. (:1. E21B 43/16 [57] ABSTRACT [58 Field Of Search 166/273, 274,275; A miscible flooding Process for the recovery of Oil 252 5 5 D fromsubterranean petroleum reservoirs containing excessive amounts ofmonovalent and polyvalent metal [56] References Cited salts in which aspecially formulated soluble oil is in- UNITED STATES PATENTS jectedinto the reservoir through one or more injection wells, and thereafterdisplaced through the reservoir g et towards one or more spacedproduction wells by the 51 I 0/1967 l' 166675 subsequent injection of anaqueous flooding medium. 314771511 11/1969 Jones et 61. :1: 166/275 Thesoluble compries an admixture of a liquid 3.480980 11/1969 Murphy 4166075 drocarbon, surface active alkyl aryl sulfonates, an or- 3,482,63212/1969 Holm 166/274 garlic Stabilizing agent, and an alkali metal ofammo- 3,500,923 3/1970 Reisburg 166/275 n m salt of a lf lkyl prim ryalcohol ethoxy- 3,508,612 4/1970 Reisburg et al.... 166/275 late having12 to 16 carbon atoms in the alkyl group. 3,512,586 5/l970 Holm l66/274The oluble il can be substantially anhydrous, or it 35961715 8/1971Halbenm [66/275 can contain water present in the form of a water-in-oil3,623,553 ll/197l Burdge 166/275 microemulsion 3,675,716 7/1972 Farmeret al. 166/275 3,799,264 3/1974 Cardenas et al. 166/273 17 Claims, N0Drawings MISCIBLE FLOODING PROCESS This invention relates to therecovery of oil from subterranean petroleum reservoirs, and moreparticularly to an improved miscible displacement fluid composi-' tionand miscible flooding process for the recovery of petroleum fromreservoirs containing excessive amounts of monovalent and polyvalentmetal salts.

It has long been recognized that substantial amounts of oil remainunrecovered in the reservoir at the completion of normal primaryrecovery operations. Hence, various secondary methods of recoveringadditional quantities of oil have been proposed, such as the wellknowntechnique of water flooding in which water is injected into thereservoir through an injection well to drive additional oil toward oneor more production wells spaced apart in the reservoir from theinjection well. Although an additional quantity of oil often can berecovered by waterflooding, the efficiency of the waterflood and theultimate oil recovery can be further improved by introducing a solventthat is miscible with both the connate oil and with the flood water intothe reservoir ahead of the flood water.

It is known that both substantially anhydrous soluble oils and solubleoils containing water present in the form of a water-in-oilmicroemulsion can be employed as the solvent in a miscible-flood waterdrive process. The soluble oils are generally admixtures of a liquidhydrocarbon, one or more surface active agents, and a stabilizing agent,and can contain water in an amount up to the concentration at which thewater-in-oil microemulsion inverts to an oil-in-water emulsion. A widevariety of liquid hydrocarbons such as liquefied petroleum gas (LPG),gasoline, mineral oil, lubricating oil, lubricating oil extract andother refinery byproduct oils, crude petroleum, and the like, can beemployed as the liquid hydrocarbon base. In many applications, it ispreferred to employ crude petroleum as the hydrocarbon base component.

While these soluble oil flooding processes can obtain high oilrecoveries under controlled laboratory conditions, it has been foundthat the recoveries obtainable under actual field conditions aresubstantially lower, and in some cases are reduced to the extent thatthe recovery operation is uneconomical. One major factor in the reducedrecovery efficiency is that the previously employed soluble oils areincompatible with the mineral salts in the reservoir, which oftencontain substantial amounts of monovalent and polyvalent salts, andparticularly divalent salts such as the water-soluble salts of calcium,magnesium and barium. Tests have shown that reservoirs containing brineshaving more than about 1.5 weight percent of dissolved monovalent saltsand/or more than about 0.15 weight percent of the polyvalent salts areparticularly deleterious, in that, upon contact with a water-containingsoluble oil, the brine causes water to be rejected from the soluble oil.

In the displacement process, the brine is mobilized ahead of themicellar solution and may only contact the leading edge of the solubleoil bank. If the connate brine is the only source of excessivemonovalent and polyvalent cations, this deleterious effect could becompensated for by injecting an additional small amount of soluble oil.However, most clayey consituents of the reservoir rock contain enoughexchangeable divalent cations, such as calcium, magnesium and bariumions, to materially affect the efficiency of the displacement process.On contact with the soluble oil,

these polyvalent cations are exchanged with monovalent cations in thesoluble oil. The amounts of polyvalent ions available for exchange is sogreat in many reservoirs that any practical amount of known soluble oilsinjected into the reservoir would pick up enough polyvalent ions tocause phase separation with an accompanying reduction in oil recoveryefficiency. Thus, need exists for a soluble oil composition that is notdeleteriously affected by excessive monovalent and polyvalent cationsand which can be employed in the recovery of oil from subterraneanreservoirs containing excessive quantities of monovalent and polyvalentsalts.

Accordingly, a principal object of this invention is to provide animproved miscible flooding process for the recovery of petroleum fromsubterranean reservoirs.

Another object of the invention is to provide a miscible floodingprocess for recovering oil from subterranean petroleum reservoirscontaining excessive amounts of monovalent and polyvalent metal salts.

Still another object of the invention is to provide a miscible floodingprocess for recovering increased amounts of oil from subterraneanpetroleum reservoirs containing excessive amounts of dissolvedmonovalent and polyvalent salts.

Yet another object of the invention is to provide a miscible floodingprocess for recovering oil from a reservoir in which the reservior rockcontains cationexchangeable divalent cations.

A further object of the invention is to provide an improved soluble oilcomposition that forms stable waterin-oil microemulsions in the presenceof high concentrations of monovalent and polyvalent metal salts.

A still further object of the invention is to provide an improvedsoluble oil composition that effects a high recovery of oil fromsubterranean reservoirs containing excessive amounts of monovalent andpolyvalent salts.

A yet further object of the invention is to provide an improved solubleoil composition that is relatively unaffected by contact with polyvalentmetal ions.

Other objects and advantages of the invention will be apparent from thefollowing description.

Briefly, this invention contemplates a process for recovering oil fromsubterranean petroleum reservoirs containing excessive amounts ofmonovalent and polyvalent metal salts in which a specially formulatedsoluble oil is injected into the reservoir through one or more injectionwells, and thereafter displaced through the reservoir towards one ormore spaced production wells by the subsequent injection of an aqueousflooding medium. The soluble oil comprises an admixture of a liquidhydrocarbon, surface active alkyl aryl sulfonates, an organicstabilizing agent, and an alkali metal or ammonium salt of a sulfatedalkyl primary alcohol ethoxylate containing 12 to 16 carbon atoms in thealkyl group. The soluble oil can be substantially anhydrous, or it cancontain water present in the form of a water-in-oil microemulsion. Ineither case, it has been found that the improved soluble oilcompositions of this invention form stable water-in-oil microemulsionsin the presence of high concentrations of monovalent and polyvalentmetal salts at all water contents up to the inversion concentration andprovide high recovery efficiencies when utilized as a miscibledisplacement fluid in a miscible flooding process for the recovery ofoil.

More specifically, this invention involves a flooding process in whichoil is displaced from a subterranean oil-bearing reservoir by animproved soluble oil composition. In the practice of this invention, aslug of the specially formulated soluble oil in the form of asubstantially anhydrous liquid or a water-in-oil microemulsion isinjected into the reservoir through one or more injection or input wellspenetrating the oil-bearing formation and forced through the reservoirby subsequently injected flood water toward at least one production oroutput well similarly completed in the reservoir. As the flooding mediumpasses through the reservoir, it displaces residual oil therein andmoves it into the producing well whereupon the oil can be recovered byconventional means. The injection and production wells can be arrangedin any convenient pattern designed to achieve maximum contact of theoil-bearing zones by the advancing flood front; such as the conventionalfive-spot pattern wherein a central producing well is surrounded by foursomewhat symmetrically located injection wells. Another of theconventional flooding patterns that can be employed in the practice ofthis invention is the line drive pattern in which the injection wellsare arranged in a line so that the injected flooding medium advancesthrough the formation to displace oil toward one or more spacedproduction wells that can also be arranged in a line substantiallyparallel to the line of injection wells.

The soluble oil of this invention is an oleaginous composition which hasthe ability to spontaneously emulsify with water when admixed therewith.These soluble oils comprise a liquid hydrocarbon, one or more selectedsurface active alkyl aryl sulfonates, a minor proportion of an organicliquid stabilizing agent, and an alkali metal or ammonium salt of asulfated alkyl primary alcohol ethoxylate having 12 to 16 carbon atomsin the alkyl group. The emulsions formed by the addition of water to thesoluble oil are of the water-in-oil type in that at water concentrationsless than the inversion concentration, oil is the continuous phase andthe water is dispersed in the oil in the form of very fine droplets, ormicelles, which are less than about 0.1 micron in size and usually rangein size from about 100 to 600 A. These emulsions are generallytransparent in appearance, and are stable in that they remain asmicroemulsions on aging, even though the water phase contains in excessof 1.5 weight percent of polyvalent metal salts. By transparent, it ismeant that the microemulsions do not have a cloudy or opaque appearance,even though they may contain color bodies. It is recognized of course,that some cloudiness may appear at certain concentrations withoutadversely affecting the utility of the microemulsions as miscibledisplacement agents. Emulsions of this type are designatedmicroemulsions to distinguish them from ordinary water-inoilmacroemulsions in which the lower limit of particle size of the waterdroplets is about 0.1 micron. at water concentrations above theinversion concentration, the emulsion inverts to an emulsion of theoil-in-water type in which droplets of oil are dispersed in a continuouswater phase. It is preferred that the water concentrations ofmicroemulsions of this invention be maintained below the inversionconcentration so as to prevent inversion to emulsions of theoil-in-water type.

One of the major constituents of the soluble oils in accordance withthis invention is a liquid hydrocarbon. The particular liquidhydrocarbon employed in formulating the soluble oil in part determinesthe viscosity and other properties of the soluble oil, and the mobilityof the soluble oil in the reservoir, which affect the efficiency of theoil recovery process. Suitable liquid hydrocarbons include crudepetroleum, such as crude pe-- troleum previously recovered from thereservoir, or other conveniently available crude oil; distillatepetroleum fractions such as refined or semi-refined petroleum products,such as gasoline, naphtha, stove oil, diesel and gas oil; residualproducts obtained by the distillation of lower boiling fractions from acrude oil, such as bunker fuel oil and other residual products; and lowvalue refinery byproducts, such as catalytic cycle oil, lube oilextract, and the like; and liquefied normally gaseous hydrocarbons, suchas propane, butane and LPG. While soluble oils can be prepared from anyof these hydrocarbon materials, in many applications it is preferred toemploy soluble oils compounded with crude petroleum, and particularlywith crude petroleum having a viscosity above about 1 centipoise at F.

Surface active materials which can be used are those that when admixedwith the liquid hydrocarbon cause the formation of microemulsions of thewater-on-oil type on the subsequent addition of water. Agents whichexhibit this property can be defined by their hydrophilic-lipophilicbalance and by their spreading coefficients. The hydrophilic-lipophilicbalance is in indication of the size and strength of the hydrophilic, orwater-loving, or polar groups, and the lipophilic, or oil-loving, ornon-polar groups in a surfactant material expressed by a numerical valuedesignated HLB number. The spreading coefficient is an indication of thefacility with which one liquid spreads upon another liquid. Spreadingcoefficients greater than 0 indicate that the first liquid will spreadon the second, and coefficients less than 0 indicate that thesupernatant liquid will simply fonn floating lenslike drops.Accordingly, surface active materials possessing the ability tospontaneously emulsify water in oil exhibit average HLB numbers of about3 to 7, and the most negative spreading coefficient consistent with thesystem.

A number of surface active materials that exhibit the ability tospontaneously emulsify oil and water to produce water-in-oilmicroemulsions are commercially available. Among the preferred agentsare various preferentially oil-soluble anionic surfactants such as thehigher alkyl aryl sulfonates. A particularly preferred surface activeagent is an alkyl aryl monosulfonate prepared by sulfonation of anaromatic petroleum fraction. These sulfonates are preferably in the formof their sodium salts, however, other salts can be used.

It has been found that superior soluble oil compositions can be preparedby employing as the surface active agent in combination ofpreferentially oil-soluble organic sulfonates and preferentiallywater-soluble organic sulfonates.

The preferentially oil-soluble surfactant material is an oil-soluble,relatively water-insoluble organic sulfonate that exhibits substantiallygreater solubility in oil than in water. Some of the preferentiallyoil-soluble organic sulfonates useful in the practice of this inventionare almost completely insoluble in water, while others exhibit limitedwater solubility, particularly at elevated temperatures. Even though thepreferentially oil-soluble organic sulfonates may exhibit some watersolubility, they are nevertheless characterized by markedly greatersolubility in oil. The preferentially water-soluble surfactant materialis a water-soluble, relatively oilinsoluble organic sulfonate thatexhibits substantially greater solubility in water than in oil. Some ofthese preferentially water-soluble organic sulfonates are almostcompletely insoluble in oil, while others exhibit limited oilsolubility, particularly at elevated temperatures. Even though thepreferentially water-soluble organic sulfonates may exhibit some oilsolubility, they are nevertheless characterized by markedly greater solubility in water.

One class of preferentially oil-soluble organic sulfonates particularlyuseful in the practice of this invention is the oil-soluble alkyl arylsulfonates that contain only one sulfonic group attached to an alkylaryl hydrocarbon. The preferentially oil-soluble alkyl aryl sulfonatesare those which in the form of their sodium salts have average molecularweights of more than about 400. Among the preferred preferentiallyoil-soluble organic sulfonates are alkyl sodium benzene sulfonates andalkyl sodium polyaryl sulfonates having molecular weights of more thanabout 400. The preferred preferentially water-soluble organic sulfonatesinclude watersoluble alkyl aryl sulfonates. The water-soluble alkyl arylsulfonates are generally those which in the form of their sodium saltshave average molecular weights of less than about 400 or which containmore than one sulfonic acid group per molecule, i.e., the preferredwater-soluble sulfonates are monosulfonates or polysulfonates which inthe form of their sodium salts have average equivalent weights of lessthan about 400. It has been found that in soluble oils compounded frompetroleum crude oil or other high boiling hydrocarbons, superior resultsare obtained by employing as the preferentially oil-soluble organicsulfonate an alkyl aryl sulfonate which in the form of its sodium salthas an average molecular weight above about 450, and preferably in therange of about 450 to 550.

Thus, the soluble oil compositions of this invention are prepared byadmixing into the hydrocarbon a preferentially oil-soluble organicsulfonate, such as an alkyl aryl sulfonate or mixture of sulfonateswhich in the form of their sodium salts have average molecular weightsof more than about 400, and a preferentially water-soluble organicsulfonate, such as an alkyl aryl monosulfonate or mixture ofmonosulfonates which in the form of their sodium salts have molecularweights of less than about 400 or such as alkyl aryl polysulfonateshaving average equivalent weights of less than about 400. Alternatively,a mixture of preferentially water-soluble and preferentially oil-solublesulfonates can be employed, such as a mixture of alkyl aryl sulfonateswhich in the form of the sodium salt have an average molecular weight inthe range of about 400 to 500 and which include both preferentiallyoil-soluble and preferentially water-soluble sulfonates.

The preferentially oil-soluble alkyl aryl sulfonates and preferentiallywater-soluble alkyl aryl sulfonates useful in the practice of thisinvention can be prepared by sulfonating an appropriate alkyl arylhydrocarbon or mixture of hydrocarbons. Thus, a preferred preferentiallyoil-soluble alkyl aryl sulfonate can be prepared by sulfonating an alkylaryl hydrocarbon to yield an alkyl aryl sulfonate which in the form ofits sodium salt has a molecular weight of more than about 400. Thepreferred preferentially water-soluble alkyl aryl sulfonates areprepared by selecting the alkyl aryl hydrocarbon so that whensulfonated, the resulting alkyl aryl sulfonatein the form of its sodiumsalt has a molecular weight of less than about 400, or by sulfonatingsufficiently to form polysulfonates. These sulfonates are preferably inthe form of the sodium salt, however other salts can be used, such asthe salts of other alkali metals and ammonium salts.

A readily available source of alkyl aryl sulfonates are the naturalpetroleum sulfonates produced by sulfonating a relatively narrow boilingrange mixture of petroleum hydrocarbons. Depending upon the boilingrange of the hydrocarbon fraction, on sulfonation, mixtures of alkylaryl monosulfonates are produced which may be either preferentiallywater-soluble or preferentially oil-soluble. The term natural petroleumsulfonates is a commercial designation of petroleum sulfonates which areobtained by a treatment of petroleum fractions, particularly solventtreated aromatic fractions, with sulfuric acid, fuming sulfuric acid orsulfur trioxide. Upon sulfonation, two types of general products areformed which are designated mahogany acid sulfonates and green acidsulfonates. The terminology is based on the colors imparted to thesulfonates in solution, a brownish color being imparted to thesulfonates which remain in the oil and the greenish color imparted toaqueous solutions made from the acid sludges formed in the sulfonationprocess. The mahogany sulfonates are preferentially oil-soluble and thegreen sulfonates are preferentially water-soluble.

The mahogany sulfonates are alkyl aryl sulfonates which usually containonly one sulfonic group per molecule and both the green and the mahoganytypes contain mixtures of sulfonates of varying molecular weights withthe mahogany, or oil-soluble sulfonates generally containing thesulfonates of higher molecular weights. The green sulfonates, orwater-soluble sulfonates, contain the sulfonates of lower molecularweight or those containing more than one sulfonate group per molecule.

The preferentially oil-soluble surface active material and thepreferentially water-soluble surface active material are employed in theproportions of about 1 part of preferentially oil-soluble agent per partof water-soluble agent to about 15 parts of oil-soluble agent per partof water-soluble agent, or more preferably to about 12 parts ofoil-soluble agent per part of watersoluble agent. That is, the solubleoil compositions of this invention contain between about 1 to 15, or 1to 12 parts of preferentially oil-soluble sulfonate per part ofpreferentially water-soluble sulfonate. Although the optimum sufactantcombination is dependent upon the characteristics of the particularreservoir, in many operations it is found that superior results areobtained with a surfactant combination containing about 1 to 4 parts ofpreferentially oil-soluble surface active material per part ofpreferentially water-soluble surface active material; and moreparticularly, with a surfactant mixture containing about 2 parts ofpreferentially oilsoluble agent per part of preferentially water-solubleagent.

The various stabilizing agents that are admixed with the soluble oil toimprove the properties and stability of the resulting microemulsionsformed by admixing the soluble oil with water include partiallyoxygenated hydrocarbons such as monohydric and polyhydric alcohols,ketones, ethers, and polyhydric alkyl ethers. More specifically, thestabilizing agents are monohydric aliphatic alcohols having 3 to 5carbon atoms, dihydric aliphatic alcohols containing 2 to 3 carbonatoms, aliphatic ketones containing 4 to 6 carbon atoms, glycol ethercontaining 4 to 10 carbon atoms, and dialkylene glycols containing 4 to6 carbon atoms. Exemplary monohydric alcohols include propyl alcohol,isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, secondary butylalcohol, tertiary butyl alcohol, normal amyl alcohol and secondary amylalcohol. Exemplary polyhydric aliphatic alcohols include ethyleneglycol, 1,3- propanediol and 1,2-propanediol. Exemplary aliphaticketones include methyl ethyl ketone, diethyl ketone and methyl isobutylketone. Exemplary glycol ethers include ethylene glycol monoethyl ether(cellosolve solvent), ethylene glycol monobutyl ether (butyl Cellosolvesolvent), diethylene glycol monobutyl ether (butyl Carbitol solvent),diethylene glycol monoethyl ether (Carbitol solvent), diethylene glycolhexyl ether (hexyl Carbitol solvent) and ethylene glycol hexyl ether(hexyl Cellosolve solvent). The terms Cellosolve and Carbitol aretrademarks of the Union Carbide Corporation. Exemplary dialkyleneglycols include diethylene glycol and dipropylene glycol. Specificagents found particularly useful include isopropyl alcohol, secondarybutyl alcohol, methyl ethyl ketone, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, anddiethylene glycol hexyl ether.

The alkali metal or ammonium salt of a sulfated alkyl primary alcoholethoxylate incorporated into the soluble oil composition ischaracterized by the following formula:

wherein R is a straight or branched chain alkyl radical containing about12 to 16 carbon atoms; n is an integer having a value of from about 2 to6; and M is an alkali metal or ammonium cation, exemplary of which aresodium, potassium, lithium and ammonium cations. The number of carbonatoms in the alkyl chain has been found to be critical, in thatethoxylates containing less than about 12 or more than about 16 carbonatoms in the alkyl group are much less efficient in forming stablemicroemulsions with water containing excessive amounts of dissolvedmonovalent or polyvalent metal ions.

The soluble oil compositions of this invention can be prepared by any ofthe conventional techniques. One suitable method is to prepare asubstantially anhydrous soluble oil by admixing the hydrocarbon basestock, the stabilizing agent and the preferentially oil-soluble surfaceactive material. Thereafter, the preferentially water-soluble surfaceactive material, if used, and the ethoxylate are added. Water-in-oilmicroemulsions can be prepared by simply adding a desired amount ofwater to the substantially anhydrous soluble oil. Preferably, the wateremployed in forming the microemulsion is a salt-containing fresh waterhaving a dissolved salt content of less than about 15,000 ppm, and morepreferably less than about 5,000 ppm. Water-soluble salts of amonovalent metal can be added to obtain a water having a desired saltcontent.

The compositions of this invention comprise a mixture of about 35 to 90volume percent of liquid hydrocarbon, such as crude petroleum; 0.5 to 8volume percent of stabilizing agent, such as one of the abovedescribedpartially oxygenated organic liquids, or a mixture of these liquids; and4 to 30 volume percent of surface active alkyl aryl sulfonates, andpreferably surface active materials containing both preferentiallyoilsoluble and preferentially water-soluble organic sulfonates in thepreviously disclosed proportions. The ethoxylate is employed in anamount proportional to the alkyl aryl sulfonate and in an amountequivalent to about 0.1 to 1.5 parts by weight of ethoxylate per part ofalkyl aryl sulfonate, and more preferably from about- 0.25 to 0.67 partsof ethoxylate per part of sulfonate. This composition can also containwater present as a water-in-oil microemulsion in an amount up to thatamount causing inversion to an oil-in-water emulsion, which is typicallyat least about 50 volume percent. Also, where the liquid hydrocarbon hasa relatively high viscosity, an additional quantity of low viscosity,light liquid hydrocarbon can be added to increase the mobility of theresulting soluble oil to obtain a more favorable mobility ratio betweenthe soluble oil and the following drive fluid. The light hydrocarbonwill usually not constitute more then about 25 volume percent of theresulting soluble oil.

In the practice of the oil recovery method of this invention, thesoluble oil is injected into the reservoir through one or more injectionwells in an amount sufficient to establish in the reservoir a bank whichcan be displaced through a reservoir. Satisfactory oil recoveries canusually be obtained by the injection of 0.01 to 0.15 reservoir porevolume of soluble oil. Aqueous flooding medium is then injected todisplace the soluble oil toward at least one production well spacedapart in the reservoir, from which fluids are produced in conventionalmanner. The aqueous flooding medium can comprise water or brine, and canbe made more viscous by the addition of a thickening agent such assugar, dextran, carboxymethyl cellulose, amines, glycerine, guar gum,and mixtures of these agents. Also, the aqueous flooding medium can berendered more viscous by the addition of a small amount of a watersoluble polymer, such as hydroxyethyl cellulose or polyacrylamide, andparticularly a partially hydrolyzed polyacrylamide. In a preferredmethod of practicing this invention, thickening agent is added to onlyan initial portion of the flood water. Thus, in this preferredembodiment, 0.01 to 0.15 reservoir pore volume of soluble oil isinjected into the reservoir and followed by 0.01 to 0.5 reservoir porevolume of thickening aqueous flooding medium. Thereafter, water or brineis injected to drive the previously injected fluids toward at least onespaced production well.

In one preferred mode of practicing the invention, 0.01 to 0.15 porevolume of substantially anhydrous soluble oil is injected into theformation and followed directly by the injection of low-salt contentwater in an amount not exceeding the volume of soluble oil injected, orthese fluids can be injected as a series of alternate slugs ofsubstantially anhydrous soluble oil and low-salt content water. Theinjected fluids are displaced through the formation by injecting asubstantially larger volume of thickened aqueous flooding mediumfollowed by flood water or brine.

The term low-salt content water is meant to include fresh water having alow-salt content, and more particularly fresh water having a less than1.0 weight percent total dissolved salts. Further, it is preferred thatthe low-salt content water contain less than 0.6 weight percent (6000ppm) of total dissolved salts. Also, the salts of polyvalent metals,such as calcium and magnesium, are particularly detrimental and it ispreferred that the low-salt content water have a low polyvalent metalsalt content. In particular, it is preferred that this water containsless than 0.1 weight percent (1000 ppm) salts of polyvalent metals, andmore preferably, less than 0.01 weight percent ppm) of these salts.

The term substantially anhydrous as used herein is meant to includesoluble oils having not more than minor amounts of water. Moreparticularly, these soluble oils contain less than 10 volume percent ofwater, and preferably less that about volume percent. Some of theingredients from which the substantially anhydrous soluble oils arecompounded, such as the liquid hydrocarbon, the stabilizing agent, andthe petroleum sulfonates, can contain moderate amounts of water, and itis difficult and costly to dehydrate these agents to remove all tracesof water. Also, it maybe advantageous when compounding the soluble oilto add a small amount of water to the composition. These substantiallyanhydrous soluble oils are to be distinguished from the high watercontent microemulsions containing substantial quantities of water, suchas from about to 50 percent or more.

The compositions of this invention can also be employed to improve thewater injectivity of water injection wells by removing oil from thereservoir immediately adjacent to the injection well, and to reducewater blockage and to remove organic sludge from the formationimmediately surrounding a producing well. In the practice of thisembodiment of the invention, about 0.5 to 3 barrels of substantiallyanhydrous soluble oil or water-in-oil microemulsion per foot offormation to be treated is introduced into the well. Fresh water orliquid hydrocarbon can then be injected into the well to displace thesoluble oil into the formation surrounding the well. Preferably, thewell is allowed to soak for a period of about 2 to 12 hours, and thenreturned to production. This treatment effectively removes water andorganic sludge from the wellbore and from the formation immediatelysurrounding the well, thereby effecting increased permeability.

The soluble oils of this invention also can be conveniently formulatedby first preparing an additive concentrate containing the surface activeagents and the stabilizing agent. The soluble oil can then be preparedsimply by mixing appropriate quantities of the additive concentrate anda selected liquid hydrocarbon, such as crude oil, and then, if desired,adding water to form a water-in-oil microemulsion. The additiveconcentrate is an admixture of preferentially oil-soluble, surfaceactive alkyl aryl sulfonate, 0.1 to 1.5 parts by weight of an alkalimetal or ammonium salt of a sulfated alkyl primary alcohol ethoxylatecontaining 12 to 16 carbon atoms in the alkyl group per part ofsulfonate, and stabilizing agent in the proportion of l to 12 parts byvolume of sulfonate per part of stabilizing agent, and preferably about2 to 7 parts by volume of sulfonate per part of stabilizing agent. Also,the concentrate can contain preferentially water-soluble surface activealkyl aryl sulfonates in the proportion of about 1 to 15, and morepreferably, 1 to 4 parts by volume of oil-soluble sulfonate per part ofwater-soluble sulfonate.

The invention is further described by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limit ing the scope of the invention as defined by theappended claims.

EXAMPLE 1 A series of soluble oil compositions, identified ascompositions 1A, 1B, 1C and ID, are prepared by admixing variousproportions of a 39 API Texas crude oil; preferentially oil-soluble,surface active, alkyl aryl petroleum monosulfonates marketed by theSonneborne Division of Witco Chemical Company, Inc. under the trademarkPetronate Rl-IL; preferentially water-soluble, surface active, alkylaryl petroleum sulfonates marketed by the Sonneborn Division of WitcoChemical Company, Inc. under the trademark Pyronate 30; ethylene glycolmonobutyl ether marketed by Union Carbide Company under the trademarkbutyl Cellosolve solvent; and a salt of a sulfated primary alcoholethoxylate. Petronate RHL is an oil solution containing about 62 percentof mixed preferentially oilsoluble alkyl aryl sodium sulfonates havingan average molecular weight in the range of 490-5 10 and not more thanabout 5 percent water. Pyronate 30 is an aqueous solution containing 30percent preferentially water-soluble alkyl aryl sulfonates having amolecular weight in the range of 330-350.

Composition 1A does not contain the ethoxylate. Compositions 1B and 1Ccontain an aqueous alcoholic solution of about 50 percent by weightammonium lauryl polyethoxy sulfate and 9 percent by weight of an amidebuilder marketed by the Proctor and Gamble Company under the trademarkOrvus K Liquid detergent. composition 1D contains a C C alkyl triethoxysodium sulfate marketed by the Shell Chemical Company under thetrademark Neodol 25-38. The proportions of ingredients employed in thesecompositions are reported in Table I.

TABLE 1 SOLUBLE OIL COMPOSITIONS Water containing 1,200 ppm of Na+ ionand 120 ppm of Ca-H- and Mg++ ions is incrementally added to soluble oil1A. Clear, stable, low-viscosity microemulsions are formed at eachincremental water concentration from 0 to percent water. This test isrepeated using brine containing 9.000 ppm of Na+ ion and 1,250 ppm ofCa-l-land Mg-l-lions. Clear, stable microemulsions are formed at waterconcentrations below about 8 percent. However, at water concentrationsabove about 8 percent, cloudy macroemulsions are produced that separateinto two phases on standing quiescent for about one hour. The brine isalso incrementally added to soluble oils 1B, 1C and 1D. Stablemicroemulsions are formed over a wide range of water constructions. Theresults of these tests are summarized in Table 2.

TABLE 2 Range of Water-Contents That "Contains 1,200 ppm Na+ ion and ppmCa-H- and Mg-H- ions. Contains 9,000 ppm Na+ ion and L250 ppm Ca-l+ andMg+lions. Contains 15.000 ppm Na+ ion and 1,250 ppm Ca-H- and Mg-H-ions.

EXAMPLE 2 A soluble oil is prepared substantially in accordance with themethod described in Example 1 by admixing 76.9 volume percent of crudeoil, 8.8 volume percent of RHL Petronate, 5.5 volume percent of Pyronate30, 1.4 volume percent of butyl Cellosolve, and 7.4 volume percent of anaqueous alcoholic solution containing about 60 percent of C -C alkylpolyethoxy ammonium sulfate marketed by the General Analine and FilmCorporation under the trademark Alipal CD-128. A brine containing 9,000ppm of Na+ ion and 1,250 ppm of Ca-l-land Mg-l-lions is incrementallyadded to the soluble oil. A clear, stable microemulsion is formed atwater concentrations below about percent. However, at waterconcentrations above about 15 percent, cloudy macroemulsions are formedthat separate into two phases on standing under quiescent conditions.

This test demonstrates the criticality of the number of carbon atoms inthe alkyl group of the alkyl polyethoxy ammonium sulfate. TheAlipalCD-l28 containing C -C alkyl polyethoxy ammonium sulfate is much lesseffective than the C C alkyl polyethoxy sulfates employed in Example 1.

EXAMPLE 3 Three substantially identical, 2-inch square by 4-foot long,Dundee sandstone test cores are first saturated with a synthetic brinecontaining 7.5 weight percent sodium chloride, 1.5 weight percentcalcium chloride and 0.4 weight percent magnesium chloride, and thenwith crude oil. The cores are then flooded with brine to residual oilsaturation. The improved oil recovery obtainable from reservoircontaining excessive amounts of monovalent and polyvalent ions with thesoluble oil compositions of this invention is demonstrated by thefollowing tests which simulate a tertiary recovery operation in an oilreservoir previously subjected to water flooding.

Three soluble oil compositions, identified as compositions 3A, 3B and 3Care prepared by admixing the following ingredients in the recitedproportions:

The flooding operation is conducted by injecting 0.03 pore volume of anaqueous polymer solution prepared by dissolving 0.05 weight percent of awater-soluble partially hydrolyzed polyacrylamide marketed by the DowChemical Company under the trademark Pusher 700 in tap water. Next, asmall quantity of the selected soluble oil, i.e., 0.03 pore volume ofcomposition 3A or 0.02 pore volume of compositions 3B or 3C, is injectedand displaced through the core by the subsequent injection of asynthetic brine containing 7.5 weight percent of sodium chloride, 1.5weight percent of calcium chloride, and 0.4 weight percent of magnesiumchloride. The produced fluids are recovered and 12 the oil recoverydetermined. The results of these testsare summarized in Table 3.

These tests demonstrate the higher oil recoveries obtainable from highsalt-content reservoirs with the soluble oil composition of thisinvention, even though smaller soluble oil slugs are employed.

EXAMPLE 4 A series of oil recovery tests were conducted on two differentcores to demonstrate the superior oil recovery obtainable in highsalt-content systems with the improved soluble oil compositions of thisinvention. The cores employed in these tests are l /z-inch square by 4-foot long Berea sandstone and 2-inch square by 4-foot long Boisesandstone. In each test, the cores are first saturated with a syntheticbrine containing 7.5 weight percent of sodium chloride, 1.5 weightpercent of calcium chloride and 0.4 weight percent of magnesiumchloride, and then with a 39 API Illinois crude oil. The oil-saturatedcores are then flooded with brine to residual oil saturation.

Three soluble oil compositions, identified as compositions 4A, 4B and 4Care prepared by admixing the following ingredients in the recitedpropositions:

Composition, Vol

4A 4B 4C 39 APl lllinois Crude Oil 470 41.3 41.3 Petronate RHL 7.0 6.96.9 Pyronate 30 4.4 4.3 4.3 Butyl Cellosolve 1.6 1.1 1.1 Fresh Water40.0 Water containing 2.3 wt. NaCl, 40.0 40 0 0.5 wt. CaCl and MgClOrvus K Liquid detergent 6.4 Sipon ES 6.4

The flooding operation is conducted by injecting a specified smallamount of a selected soluble oil, i.e., 0.03 pore volume of soluble oil4A or 0.02 pore volume of soluble oils 4B or 4C. The injected solubleoil is then displaced through the core by the subsequent injection of anaqueous polymer solution prepared by dissolving 0.15 weight percent ofPusher 700 polymer in tap water. The produced fluids are recovered andthe oil recovery determined. The results of these tests are summarizedin Table 4.

13 These tests demonstrate that higher oil recoveries can be obtainedfrom reservoirs containing excessive amounts of metal salts with thesoluble oil compositions of this invention than can be obtained with 50percent larger quantities of conventional soluble oil compositions.

EXAMPLE A series of soluble oil compositions are prepared by admixing68.9 volume percent of Illinois crude oil, 1 1.4 volume percent ofPetronate RHL sulfonate, 7.0 volume percent of Pyronate 30 sulfonate,2.1 volume per cent of butyl Cellosolve solvent, and 10.6 volume percentof a selected, commercially available, alkali metal or ammonium salt ofa sulfated alkyl primary alcohol ethoxylate. A synthetic brinecontaining 2.3 weight percent of sodium chloride and 0.5 weight percentof calcium and magnesium chloride is added to each of the soluble oilsin incremental portions, and the appearance of the resultingmicroemulsion observed at each increment of water addition and the brinetolerance of the soluble oil determined. The brine tolerance of asoluble oil is defined as the maximum volume percent of brine that canbe added to the soluble oil to form stable microemulsions. These dataare summarized in Table 5.

EXAMPLE 6 A soluble oil additive concentrate is prepared by admixing anoil solution containing about 62 percent of preferably oil-soluble alkylaryl sufonates having an average molecular weight in the range of490-510, about 0.8 parts by weight of sodium salt of a sulfated C Calkyl primary alcohol ethoxylate per part of sulfonate, and secondarybutyl alcohol in the proportion of 5 parts by volume of the sulfonateper part of stabilizing a ent.

A soluble oil is prepared by admixing 100 parts of the additiveconcentrate prepared in the above step with 370 parts by volume of crudepetroleum and 20 parts by volume of water.

EXAMPLE 7 A soluble oil additive concentrate is prepared by admixing anoil solution containing about 62 percent of preferably oil-soluble alkylaryl sulfonates having an average molecular weight in the range of490-510, about 0.25 parts by volume of an aqueous solution containing 30percent preferentially water-soluble petroleum sulfonates having anaverage molecular weight in the range of 330-350 per part of oil-solublesufonate, about 0.6 parts by weight of sodium salt of a sulfated C -Calkyl primary alcohol ethoxylate per part of sulfonate, and ethyleneglycol hexyl ether in the proportion of 5 parts by volume of thesulfonate per part of stabilizing agent.

A soluble oil is prepared by admixing 100 parts of the additiveconcentrate prepared in the above step with 370 parts by volume of crudepetroleum and 200 parts by volume of water.

Various embodiments and modifications of this invention have beendescribed in the foregoing description and examples, and furthermodifications will be apparent to those skilled in the art. Suchmodifications are included within the scope of this invention as definedby the following claims.

Having now described the invention, I claim:

1. In the method for recovering petroleum from a subterranean reservoircontaining excessive amounts of metal cations in which a soluble oilmiscible with both the connate reservoir oil and with water is injectedinto the reservoir through an injection well, and thereafter an aqueousflooding medium is injected to drive the miscible displacement fluidtowards a spaced production well from which fluids are recovered, theimprovement which comprises employing a soluble oil comprising anadmixture of a liquid hydrocarbon, preferentially oil-soluble surfaceactive alkyl aryl sulfonates, a liquid organic stabilizing agent, and asulfated surfactant comprising an admixture of ammonium laurylpolyethoxy sulfate having 2 to 6 ethoxy groups and an amide builder.

2. The method defined in claim 1 wherein said soluble oil comprises anadmixture of about 35 to volume percent of said liquid hydrocarbon, 0.5to 8 volume percent of said stabilizing agent, 4 to 30 volume percent ofsaid alkyl aryl sulfonates, and 0.1 to 1.5 parts by weight of saidsulfated surfactant per part of sulfonate.

3. The method defined in claim 1 wherein said soluble oil comprises anadmixture of about 35 to 90 volume percent of said liquid hydrocarbon,0.5 to 8 volume percent of said stabilizing agent, 4 to 30 volumepercent of a mixture of preferentially oil-soluble and preferentiallywater-soluble surface active alkyl aryl sulfonates in the proportions ofabout 1 to 15 parts by weight of oil-soluble sulfonate per part ofwater-soluble sulfonate, and 0.1 to 1.5 parts by weight of said sulfatedsurfactant per part of sulfonate.

4. The method defined in claim 1 wherein said liquid hydrocarbon iscrude petroleum.

5. The method defined in claim 4 wherein said soluble oil also containsan additional quantity of light liquid hydrocarbon to increase themobility of the miscible displacement fluid to obtain a more favorablemobility ratio between the soluble oil and the following aqueousflooding medium.

6. The method defined in claim 1 wherein said soluble oil contains waterpresent in the form of a water-inoil microemulsion.

7. The method defined in claim 1 wherein between about 0.01 and 0.15reservoir pore volume of miscible displacement fluid is injected intothe reservoir.

8. The method defined in claim 1 wherein at least an initial portion ofsaid aqueous flooding medium is increased in viscosity by the additionof a thickening agent.

9. The method defined in claim 1 wherein said soluble oil issubstantially anhydrous and wherein small slugs of said soluble oil andlow salt-content water are alternately injected into the reservoir.

10. A method for recovering petroleum from a subterranean reservoirpenetrated by an injection well and a production well spaced apart inthe reservoir, which comprises:

injecting 0.01 to 0.15 reservoir pore volume of a 801- 10 uble oilcomprising a mixture of 1) about 35 to 90 volume percent of liquidhydrocarbon; (2) about 0.5 to 8 volume percent of an organic liquidstabilizing agent selected from the group consisting of monohydricaliphatic alconols having 3 to 5 carbon atoms, alcohols aliphaticalcohols having 2 to 3 carbon atoms, aliphatic ketones having 4 to 6carbon atoms, glycol ethers having 4 to 10 carbon atoms, and dialkyleneglycols having 4 to 6 carbon atoms; (3) about 4 to 30 volume percent ofa mixture of preferentially oil-soluble and preferentially water-solublesurface active alkyl aryl sulfonates in the proportion of about 1 toparts by weight of oil-soluble sulfonate per part of water-solublesulfonate; (4) about 0.1 to 1.5 parts by weight of a sulfated surfactantper part of sulfonate, said sulfated surfactant comprising an admixtureof ammonium lauryl polyethoxy sulfate having 2 to 6 ethoxy groups and anamide builder; and (5 from about 0 to 50 volume percent of water presentin the form of a water-in-oil microemulsion;

thereafter injecting an aqueous flooding medium to drive the soluble oiltowards a spaced production well, at least an initial portion of saidaqueous flooding medium being increased in viscosity by the addition ofa thickening agent; and recovering petroleum from said production well.

11. The method defined in claim 10 wherein said liquid hydrocarbon iscrude petroleum.

12. The method defined in claim 11 wherein said soluble oil alsocontains an additional quantity of light liquid hydrocarbon to increasethe mobility of the miscible displacement fluid to obtain a morefavorable mobility ratio between the soluble oil and the followingaqueous flooding medium.

13. the method defined in claim 10 wherein said soluble oil issubstantially anhydrous and wherein small slugs of said soluble oil andlow salt-content water are alternately injected into the reservoir.

14. The method defined in claim 10 wherein said preferentiallyoil-soluble alkyl aryl sulfonates are alkyl aryl monosulfonates which inthe form of their sodium salts have an average molecular weight aboveabout 400 and said preferentially water-soluble alkyl aryl sul-- fonatesare alkyl aryl monosulfonates having an average molecular weight of lessthan about 400 or are alkyl aryl polysulfonates.

15. A method for recovering petroleum from a subterranean reservoirpenetrated by an injection well and a production well spaced apart inthe reservoir, which comprises:

injecting 0.01 to 0.15 reservoir pore volume of a soluble oil comprisinga mixture of (1) about 35 to volume percent of crude petroleum; (2)about 0.5 to 8 volume percent of an organic liquid stabilizing agentselected from the group consisting of secondary butyl alcohol, ethyleneglycol monoethyl ether, ethylene glycol monobutyl ether, diethyleneglycol monoethyl ether, diethylene glycol hexyl ether and ethyleneglycol hexyl ether; (3) about 4 to 30 volume percent of a mixture ofpreferentially oil-soluble surface active alkyl aryl monosulfonates thatin the form of their sodium salts have average molecular weight aboveabout 400 and preferentially water-soluble surface active alkyl arylmonosulfonates that in the form of their sodium salts have averagemolecular weights below about 400 and/or preferentially water-solublesurface active alkyl aryl polysulfonates, said sulfonates being presentin the proportional of about 1 to 15 parts by weight of oil-solublesulfonate per part of water-soluble sulfonate; (4) about 0. 1 to 1.5parts by weight of a sulfated surfactant per part of sulfonate, saidsulfated surfactant comprising an admixture of ammonium laurylpolyethoxy sulfate having 2 to 6 ethoxy groups and an amide builder; and(5) from about 0 to 50 volume percent water present in the form of awater-in-oil microemulsion;

thereafter injecting an aqueous flooding medium to drive the soluble oiltowards a spaced production well, at least an initial portion of saidaqueous flooding medium being increased in viscosity by the addition ofa thickening agent, and

recovering petroleum from said production well.

16. The method defined in claim 15 wherein said soluble oil alsocontains an additional quantity of light liquid hydrocarbon to increasethe mobility of the miscible displacement fluid to obtain a morefavorable mobility ratio between the soluble oil and the followingaqueous flooding medium.

17. The method defined in claim 15 wherein said soluble oil issubstantially anhydrous and wherein small slugs of said soluble oil andlow salt-content water are alternately injected into the reservoir.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,920,073

DATED November 18 1975 INVENTORQZ) LeRoy w. Holm It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown betow:

In Claim 10, column 15, line l r, "alconols" should be corrected to read-alcohols-;

and in line 15, "alcohols", first occurrence, should be corrected toread -dihydric--.

Signed and Sealed this twenty-fourth Of February 1976 [SEAL] A ttest:

RUTH- C. MASON C. MARSHALL DANN Alrestmg ()jfrcer (ummixsr'mn'rujlarenrs and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICECERTIFICATE OF CORRECTION Q PATENT NO. 3,920,073

DATED November 18, 1975 INVENTORQZ) LeRoy W. Holm It is certified thaterror appears in the above-identified patent and that said LettersPatent 6 are hereby corrected as shown below:

In Claim 10 column 15 line 1 "alconols" should be corrected to readalcohols--; and in line 15, "alcohols", first occurrence, should becorrected to read -dihydric-.

lgncd and Scaled this twenty-fourth Day of February 1976 i [SEAL] lArrest:

RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner vfParenlsand Trademarks Q

1. IN THE METHOD FOR RECOVERING PETROLEUM FROM A SUBSTERRANEAN RESERVOIRCONTAINING EXCESSIVE AMOUNTS OF METAL CATIONS IN WHICH A SOLUBLE OILMISCIBLE WITH BOTH THE CONNATE RESERVOIR OIL AND WITH WATER IS INJECTEDINTO THE RESERVOIR THROUGH AN INJECTION WELL, AND THEREAFTER AN AQUEUSFLOODING MEDIUM IS INJECTED TO DRIVE THE MISCIBLE DISPLACEMENT FLUIDTOWARDS A SPACED PRODUCTION WELL FROM WHICH FLUIDS ARE RECOVERED, THEIMPROVEMENT WHICH COMPRISES EMPLOYING A SOLUBLE OIL COMPRISING ANADMIXTURE OF A LIQUID HYDROCARBON, PREFERENTIALLY OIL-SOLUBLE SURFACEACTIVE ALKYL ARYL SULFONATES, A LIQUID ORGANI STABILIZING AGENT, AND ASULFONATED SURFACTANT COMPRISING AN ADMIXTURE OF AMMONIUM LAURYLPOLYETHOXY SULFATE HAVING 2 TO 6 ETHOXY GROUPS AND AN AMIDE BUILDER. 2.The method defined in claim 1 wherein said soluble oil comprises anadmixture of about 35 to 90 volume percent of said liquid hydrocarbon,0.5 to 8 volume percent of said stabilizing agent, 4 to 30 volumepercent of said alkyl aryl sulfonates, and 0.1 to 1.5 parts by weight ofsaid sulfated surfactant per part of sulfonate.
 3. The method defined inclaim 1 wherein said soluble oil comprises an admixture of about 35 to90 volume percent of said liquid hydrocarbon, 0.5 to 8 volume percent ofsaid stabilizing agent, 4 to 30 volume percent of a mixture ofpreferentially oil-soluble and preferentially water-soluble surfaceactive alkyl aryl sulfonates in the proportions of about 1 to 15 partsby weight of oil-soluble sulfonate per part of water-soluble sulfonate,and 0.1 to 1.5 parts by weight of said sulfated surfactant per part ofsulfonate.
 4. The method defined in claim 1 wherein said liquidhydrocarbon is crude petroleum.
 5. The method defined in claim 4 whereinsaid soluble oil also contains an additional quantity of light liquidhydrocarbon to increase the mobility of the miscible displacement fluidto obtain a more favorable mobility ratio between the soluble oil andthe following aqueous flooding medium.
 6. The method defined in claim 1wherein said soluble oil contains water present in the form of awater-in-oil microemulsion.
 7. The method defined in claim 1 whereinbetween about 0.01 and 0.15 reservoir pore volume of miscibledisplacement fluid is injected into the reservoir.
 8. The method definedin claim 1 wherein at least an initial portion of said aqueous floodingmedium is increased in viscosity by the addition of a thickening agent.9. The method defined in claim 1 wherein said soluble oil issubstantially anhydrous and wherein small slugs of said soluble oil andlow salt-content water are alternately injected into the reservoir. 10.A method for recovering petroleum from a subterranean reservoirpenetrated by an injection well and a production well spaced apart inthe reservoir, which comprises: injectIng 0.01 to 0.15 reservoir porevolume of a soluble oil comprising a mixture of (1) about 35 to 90volume percent of liquid hydrocarbon; (2) about 0.5 to 8 volume percentof an organic liquid stabilizing agent selected from the groupconsisting of monohydric aliphatic alconols having 3 to 5 carbon atoms,alcohols aliphatic alcohols having 2 to 3 carbon atoms, aliphaticketones having 4 to 6 carbon atoms, glycol ethers having 4 to 10 carbonatoms, and dialkylene glycols having 4 to 6 carbon atoms; (3) about 4 to30 volume percent of a mixture of preferentially oil-soluble andpreferentially water-soluble surface active alkyl aryl sulfonates in theproportion of about 1 to 15 parts by weight of oil-soluble sulfonate perpart of water-soluble sulfonate; (4) about 0.1 to 1.5 parts by weight ofa sulfated surfactant per part of sulfonate, said sulfated surfactantcomprising an admixture of ammonium lauryl polyethoxy sulfate having 2to 6 ethoxy groups and an amide builder; and (5) from about 0 to 50volume percent of water present in the form of a water-in-oilmicroemulsion; thereafter injecting an aqueous flooding medium to drivethe soluble oil towards a spaced production well, at least an initialportion of said aqueous flooding medium being increased in viscosity bythe addition of a thickening agent; and recovering petroleum from saidproduction well.
 11. The method defined in claim 10 wherein said liquidhydrocarbon is crude petroleum.
 12. The method defined in claim 11wherein said soluble oil also contains an additional quantity of lightliquid hydrocarbon to increase the mobility of the miscible displacementfluid to obtain a more favorable mobility ratio between the soluble oiland the following aqueous flooding medium.
 13. the method defined inclaim 10 wherein said soluble oil is substantially anhydrous and whereinsmall slugs of said soluble oil and low salt-content water arealternately injected into the reservoir.
 14. The method defined in claim10 wherein said preferentially oil-soluble alkyl aryl sulfonates arealkyl aryl monosulfonates which in the form of their sodium salts havean average molecular weight above about 400 and said preferentiallywater-soluble alkyl aryl sulfonates are alkyl aryl monosulfonates havingan average molecular weight of less than about 400 or are alkyl arylpolysulfonates.
 15. A method for recovering petroleum from asubterranean reservoir penetrated by an injection well and a productionwell spaced apart in the reservoir, which comprises: injecting 0.01 to0.15 reservoir pore volume of a soluble oil comprising a mixture of (1)about 35 to 90 volume percent of crude petroleum; (2) about 0.5 to 8volume percent of an organic liquid stabilizing agent selected from thegroup consisting of secondary butyl alcohol, ethylene glycol monoethylether, ethylene glycol monobutyl ether, diethylene glycol monoethylether, diethylene glycol hexyl ether and ethylene glycol hexyl ether;(3) about 4 to 30 volume percent of a mixture of preferentiallyoil-soluble surface active alkyl aryl monosulfonates that in the form oftheir sodium salts have average molecular weight above about 400 andpreferentially water-soluble surface active alkyl aryl monosulfonatesthat in the form of their sodium salts have average molecular weightsbelow about 400 and/or preferentially water-soluble surface active alkylaryl polysulfonates, said sulfonates being present in the proportionalof about 1 to 15 parts by weight of oil-soluble sulfonate per part ofwater-soluble sulfonate; (4) about 0.1 to 1.5 parts by weight of asulfated surfactant per part of sulfonate, said sulfated surfactantcomprising an admixture of ammonium laurYl polyethoxy sulfate having 2to 6 ethoxy groups and an amide builder; and (5) from about 0 to 50volume percent water present in the form of a water-in-oilmicroemulsion; thereafter injecting an aqueous flooding medium to drivethe soluble oil towards a spaced production well, at least an initialportion of said aqueous flooding medium being increased in viscosity bythe addition of a thickening agent, and recovering petroleum from saidproduction well.
 16. The method defined in claim 15 wherein said solubleoil also contains an additional quantity of light liquid hydrocarbon toincrease the mobility of the miscible displacement fluid to obtain amore favorable mobility ratio between the soluble oil and the followingaqueous flooding medium.
 17. The method defined in claim 15 wherein saidsoluble oil is substantially anhydrous and wherein small slugs of saidsoluble oil and low salt-content water are alternately injected into thereservoir.